A steering wheel is generally referred to as a wheel or a handle, and is a circular steering apparatus used for changing a direction of progress by turning the wheels of a vehicle to left or right.
A steering wheel delivers rotation operating force of a driver to a steering apparatus through a steering axis binding to the center as a medium, and carries out an operation of angular motioning the wheel. Such a steering wheel has been formed with a circular rim that a driver holds, and a rim support formed in the center of this rim and having a steering axis binding to the center. A steering wheel may be formed with various materials, but may be manufactured using a method of welding a rim support to a rim that forms a metal pipe into a ring shape, or manufactured using a method of casting aluminum or magnesium, a light nonferrous metal having relatively high stiffness. To the rim support part of a steering wheel manufactured as above, an assembly of an air bag, a horn button, an audio operation button and the like are combined after being covered with a cover made of a synthetic resin material, and on the rim, a rim cover made with cloth, synthetic leather, leather and the like covers the surface of the steering wheel.
In conventional processes for preparing synthetic leather, a method of forming a film may be used by applying an urethane skin resin mixing solution containing an organic solvent such as dimethylformamide and methylethyl ketone on a release paper and drying the result, and applying an adhesive on the formed urethane film, and cross-linking and curing the result, and thus prepared skin may be combined with a conventional (short-fiber type)microfiber nonwoven fabric or a woven fabric fiber base.
In the related arts, Korean Patent Application Laid-Open Publication No. 10-2012-0133210 (Patent Document 1) discloses a method for preparing polyurethane synthetic leather for automobile interior materials, and the method for preparing polyurethane synthetic leather includes a first step of preparing a release paper; a second step of forming a surface layer laminated with a plurality of layers by repeatedly applying a polyurethane resin including water-dispersible polycarbonate urethane on the upper surface of the release paper and drying the result a plurality of times; a third step of forming an adhesion layer by applying a solventless-type adhesive on the upper surface of the surface layer; and a fourth step of forming a fabric layer by adhering woven fabric weaved with synthetic fiber, knitwork or nonwoven fabric on the upper surface of the adhesion layer.
However, the synthetic leather manufactured as described above may form a skin coating layer on a fiber base of short-fiber type nonwoven fabric or woven fabric having relatively small density, such that substantial wrinkles may be formed when such synthetic leather is used as a rim cover of a steering wheel, and sew holes may be gaped. Accordingly, there may be limitations in providing softness similar to natural leather volume, feel and the like. In addition, the conventional polyurethane skin coating layer may have light resistance for irradiation amount, which is a physical property for general vehicle sheets and door trims, of about 84 MJ but may not have sufficient light resistance for irradiation amount of about 126 MJ, which is required for steering wheel covering of a vehicle. In addition, physical properties such as chemical resistance, heat aging resistance and frictional coloration may be reduced low, such that application of the synthetic leather as a rim cover of a steering wheel has not been made.
In addition, Korean Patent No. 10-1402783 (Patent Document 2) discloses synthetic leather in which a fiber base layer containing long fiber-type high density microfiber nonwoven fabric; an urethane porous layer having micropores; and a skin layer; are laminated in consecutive order. Such technology has introduced an urethane porous layer having structurally strong binding power on long fiber-type high density microfiber nonwoven fabric thereby complementing hydrolysis resistance, heat resistance, chemical resistance and mechanical properties compared to existing synthetic leather. However, improvements in physical properties of a wrinkle property and fouling resistance may be required in order to be used for a curvy steering wheel cover.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.